1. Field of the Invention
The present invention relates to a system for controlling the transport of a film for a camera.
2. Description of Background
Some conventional film transport control systems for use in cameras are of high cost and low reliability since they employ many switches for applying signals of various detected conditions to a central processing unit.
FIG. 7 of the accompanying drawings illustrates a conventional film transport control system for use in a camera. The film transport control system generally comprises a microcomputer or central processing unit (CPU) 1, a shutter unit 2, a liquid crystal display unit 3, and a group of switches. The group of switches includes a one-frame fed switch SW1 having a movable contact actuatable by a mechanism (not shown) into contact with fixed terminal c upon completion of operation of the shutter and into contact with another fixed terminal d when one film frame is fed, a perforation switch SW2 that can be closed by each film perforation when the film is transported by a mechanism (not shown), wind/rewind changeover switches SW3a, SW3b actuatable by a mechanism (now shown) into the illustrated position when the back cover of the camera is opened and into the other position when the terminal film end is reached, i.e. when all of the film frames are exposed, a film detector switch SW4 for detecting whether the film has been fuly rewound in the film cartridge, a cartridge detector switch SW5 for detecting whether there is a film cartridge in the camera, and a back cover switch SW6 for detecting whether the back cover of the camera is opened or closed. The film transport control system additionally includes a film transport motor M for winding and rewinding the film, a DC power supply B, and resistors R1, R2, R3. The liquid crystal display unit 3 has a cartridge indicator 4, a film transport indicator 5, a take-up spool indicator 6, and an exposure counter indicator 7.
Film can automatically be loaded in the camera under the control of the film transport control system, as next described. When the film cartridge is placed in the camera and the back cover of the camera is closed, the cartridge detector switch SW5 and the back cover SW6 are closed. Based on signals from these switches SW5, SW6, the CPU 1 detects when the film cartridge is put in the camera and the back cover is closed, and applies a shutter release pulse to the shutter unit 2 to energize a shutter release magnet (not shown) for thereby releasing the shutter. Upon completion of the shutter release, the movable contact of the one-frame feed switch SW1 contacts the fixed terminal c to energize the film transport motor M to rotate in a forward direction to wind the film. When one frame of the film is fed, the movable contact of the one-frame feed switch SW1 is moved into contact with the fixed terminal d for electromagnetically braking the motor M until it is stopped. A signal is then applied from one terminal of the motor M to an input port e of the CPU 1, which detects the stoppage of the motor M and applies a shutter release pulse to energize the shutter release magnet to release the shutter again. The above cycle is repeated four times to wind the film for four frames, whereupon the automatic film loading operation is completed. The perforation switch SW2 is repeatedly turned on and off in timed relation to the film transport thus affected. For example, the perforation switch SW2 is turned on and off eight times per film frame. The CPU 1 frequency-divides by 2 the signal from the perforation switch SW2 into a signal having a half frequency, and the frequency-divided signal is applied to the film transport indicator 5 to energize a plurality of indicator elements 51 through 54 thereof successively.
The following discussion describes how it is determined whether or not the automatic film loading is successively effected. Perforation pulses are generated by the perforation switch SW2 when the fourth shutter release pulse is applied by the CPU 1 to the shutter unit 2. If seven or more perforation pulses are generated, then the CPU 1 determines that the automatic film loading procedure has been successful. The CPU 1 then energizes the take-up spool indicator 6 and at the same time displays "1" on the exposure counter indicator 7. If, however, only six or less perforation pulses are produced, then the CPU 1 determines that the automatic film loading process has been unsuccessful. The CPU 1 now causes the take-up spool indicator 6 to flicker, giving the user a loading failure warning, and locks the shutter from being released to protect the film against undesired exposure.
When a shutter release button is pressed, the CPU 1 applies a shutter release pulse to the shutter unit 2 to release the shutter and at the same time increments the count on the exposure counter indicator 7 by 1. Upon completion of the shutter release, the non-frame feed switch SW1 is shifted to the terminal c to rotate the film transport motor M in the forward direction, winding the film. After the film is advanced for one frame, the one-frame feed switch SW1 is shifted to the terminal d to stop the motor by electromagnetic braking. At this time, perforation pulses are produced by the performation switch SW2 in timed relation to the advancing movement of the film, and the CPU 1 frequency-divides the produced perforation pulses by 2. The frequency-divided pulses are applied to the liquid crystal display unit 3 for sequential energization of the indicator elements 51 through 54. Such sequential energization may be repeated, for example, in three successive cycles to allow the user to confirm that the film has properly been transported even after the winding of the film.
The film transport process and the indications on the display unit 3 are repeated as the film frames are exposed. When the terminal end of the film reaches the aperture in the camera, i.e., when all of the film frames are exposed, the wind/rewind changeover switches SW3a, SW3b are changed over to reverse the film transport motor M to rewind the exposed film. At this time, too, the CPU 1 frequency-divides perforation pulses from the perforation switch SW2 by 2 and applies the frequency-divided pulses to energize the indicator elements 51 through 54 successively. Each time eight perforation pulses are applied, the CPU 1 decrements the count on the exposure counter indicator 7 by 1.
When the film has fully been rewound into the cartridge, the film detector switch SW4 is opened to deenergize the film transport motor M to stop rewinding the film. The signals at both terminals of the film transport motor M go high in level, and such a high level is detected by the CPU 1, which then displays "E" on the exposure counter indicator 7 to apprise the user of the completion of the find rewinding process.
The conventional film transport control system shown in FIG. 7 is however disadvantageous in that it employs many switches, i.e., the one-frame feed switch SW1, the perforation switch SW2, the wind/rewind changeover switches SW3a, SW3b, the film detector switch SW4, the cartridge detector switch S5, and the back cover switch SW6, and hence is high in cost and low in reliability.